The present invention relates to a motor driven power steering system and a method of controlling the same, and more particularly, a motor driven power steering system which can be normally operated even when an error occurs in a torque sensor, and a method of controlling the same.
Examples of a power assistance steering system for reducing steering force required of a driver when steering a vehicle include a hydraulic power steering system which uses hydraulic pressure formed by a hydraulic pump to assist with the steering force of the driver, and a motor driven power steering system (hereinafter referred to as an ‘MDPS’) which uses the drive torque of an electric motor to assist with the steering force of the driver.
The MDPS functions to assist with the steering force resulting from steering wheel manipulation of the driver in such a way that the electric motor is automatically controlled depending on driving conditions of a vehicle. Therefore, the MDPS provides further enhanced steering performance and steering sensation, compared to the hydraulic power steering system.
Such an MDPS senses a vehicle speed, a steering angle and a torque, respectively, using a vehicle speed sensor, a steering angle sensor and a torque sensor, and generates a target assist torque of the motor based on the vehicle speed, the steering angle and the torque, thus assisting with the steering force.
However, in the conventional MDPS, if an error occurs in the torque sensor, a fail safe logic determines the degree of abnormality and, based on this, limits the output or converts the operating type into a manual type, whereby the steering operation may not be normally performed.
The related art of the present invention is disclosed in Korean Patent Publication No. 10-2008-0078428 (published on Aug. 27, 2008), entitled “Method of compensating for middle point of torque sensor of motor driven power steering system”.